This invention relates to a perpendicular magnetic recording disk for use in a perpendicular magnetic recording disk drive that uses a single pole head, and more particularly to an improved perpendicular magnetic recording disk with a laminated underlayer to provide a flux return path for the magnetic field from the head.
Perpendicular magnetic recording has been suggested as a promising path toward ultra-high recording densities in magnetic recording rigid disk drives. The most common type of system is one that uses a xe2x80x9cprobexe2x80x9d or single pole recording head with a xe2x80x9cdual-layerxe2x80x9d media as the recording disk. The dual-layer media comprises a perpendicular magnetic data recording layer formed on a xe2x80x9csoftxe2x80x9d or relatively low-coercivity magnetically permeable underlayer, the underlayer serving as a flux return path for the field from the pole head. This type of system is also called xe2x80x9cType 1xe2x80x9d perpendicular magnetic recording. A schematic of such a system with a read element for reading the recorded data is shown in FIG. 1.
It is desirable that the underlayer for dual-layer perpendicular recording media behave magnetically soft, and be devoid of domain walls. Magnetic xe2x80x9csoftnessxe2x80x9d, in this instance, refers to the ability of the underlayer to carry magnetic flux directly in proportion to the in-plane magnetic fields driving that flux. To achieve magnetic softness without domain walls, it is desired, in the quiescent state, absent of recorded transitions and/or writing fields, that the underlayer be effectively in a xe2x80x9csingle-domain-statexe2x80x9d, whereby the magnetization in the underlayer is everywhere aligned in predominantly a single direction. The presence of multiple domains as a source of media noise in dual-layer perpendicular media has been reported by N. R. Darragh et al., xe2x80x9cObservation of Underlayer Domain Noise in Perpendicular Recording Disksxe2x80x9d, IEEE TRANSACTIONS ON MAGNETICS, Vol. 29, No. 6, November 1993, pp. 3742-3744. To address the problem of media noise, multilayered underlayers have been proposed that comprise multiple soft magnetic films separated by electrically conductive films, such as Al and CoCr. These multilayers are described in the following references: T. Ichihara et al., xe2x80x9cImprovement of the Magnetic Characteristic of Multilayered Nixe2x80x94Fe thin Films by Supplying External In-Plane Field during Sputteringxe2x80x9d, IEEE TRANSACTIONS ON MAGNETICS, Vol. 32, No. 5, September 1996, pp. 4582-4584; and S. Nakagawa et al., xe2x80x9cSoft Magnetic and Crystallographic Properties of Ni81Fe19/Co67Cr33 Multilayers as Backlayers in Perpendicular Recording Mediaxe2x80x9d, IEEE TRANSACTIONS ON MAGNETICS, Vol. 30, No. 4, 1994, pp. 4020-4022.
What is needed is an improved dual-layer type perpendicular magnetic recording disk with an underlayer that results in less media noise.
The present invention is a dual-layer type perpendicular magnetic recording disk for use in a perpendicular magnetic recording system that uses a single pole recording head. The underlayer portion of the dual-layer disk is a laminated underlayer that has at least two ferromagnetic films exchange-coupled across an antiferromagnetic coupling layer. The magnetic moments of the ferromagnetic layers in the laminated underlayer are oriented antiparallel. The laminated underlayer provides a soft magnetically permeable flux return path without undesirable domain walls and associated media noise, with controllable permeability and minimization of saturation of the upper ferromagnetic layers. In one embodiment the moments of the ferromagnetic layers in the underlayer are oriented generally radially on the disk. In another embodiment the moments are oriented generally circumferentially in the track direction on the disk, so that the beneficial effect of the soft magnetic underlayer occurs primarily only during the writing process.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.